Not sure what the question is referring to - I am not aware of boats at the gardens.

No, I don’t recall seeing a ramp.

It’s a public park so it’s free to walk through.

There was a pond in the front of the main building with people playing with remote controlled boats however as for kids specific activities I'm not sure. We saw people lounging around in the sun, people doing Tai Chi under the trees and a band playing in the gazebo. Nice place for families to hang out inside a city

I was there in October 2019 and they were playing chess - I don't think there are permanent tables. I saw them playing in the NE corner of the park, away form the pond and places where a lot of tourists go. I have pictures but cannot see how I can upload them to you.

Парк красивый.Были в июле,поэтому не могу однозначно ответить.Смотрите по погоде.Возможно и в декабре Вам повезет.Кстати,Пантеон от парка в пешей доступности.Удачи!

In late September you would find more autumnal colours and grasses. Depending on the trees, the first leaves might be falling down. Since June and July were very hot in France, plants would have suffered and most likely few would still bloom. Still beautiful, just a different atmosphere

There is a fee. 3 Euros for children, 1 for parents

don't forget about renting the little boats for the kids to float in the middle!